1. Field of the Invention
The process of this invention resides in the area of production of silicon carbide foam and more particularly relates to a method for production of silicon carbide foam using bead-like material to form the cells of the foam and removing such bead-like material during the foam's formation.
2. Description of the Prior Art
Silicon carbide is a very strong crystalline structure having high thermal conductivity and resistance to fluxing, fusion and oxidation. It can, in some instances, be utilized as an electrical insulator but as it heats, it becomes more conductive. At 2000 degrees F. it is as conductive as graphite and is therefore classed as a semi-conductor which has many uses. Early production of silicon carbide was accomplished by heating a mixture of clay and coke in an iron bowl with a carbon arc lamp. The hexagonal crystals which attached to the carbon electrode were formed of silicon carbide. Since these crystals have the approximate hardness of diamonds, they are frequently utilized as an abrasive in industry. Today's methods of production of silicon carbide are basically the same as the historical methods. The major difference is in the size of the furnace and control of the ingredients. A furnace run will take about 36 hours during which the temperature can vary from 4,000-5,000 degrees F. in the core, dropping to about 2,500 degrees F. at the outer edge. These furnaces are usually in the shape of large troughs with electrodes at either end. The energy consumed can exceed 100,000 kilowatt hours per run. Furnaces are about 40 ft. long, 10 ft. high and 10 ft. wide and can produce about 25,000 lbs of silicon carbide per run. Silicon carbide can also be used to produce strong, lightweight members for the aerospace industry such as girders and is further useful in electro-chemical processing machinery where it is desired to have non-conductive members.
A type of foamed silicon carbide material is disclosed in U.S. Pat. No. 4,777,153 to Sonuparlak et al. Sonuparlak et al discloses a very small celled foam made from microspheres with very weak structural integrity due to its very thin cell walls. The strength of a porous structure ordinarily decreases with increased porosity. However in some cases the strength does not decrease with increasing porosity if the structure has a dense surface. Sonuparlak et al gives his structure a dense surface by slip casting or tape casting so as to add dense layers to his structure.